This research project seeks to advance our understanding of the function of the retina in two fundamental aspects of vision: (1) visual adaptation and (2) contrast vision. This will be done by analyzing the light-evoked responses of photoreceptor cells, bipolar cells, and amacrine cells in animals that offer unique opportunities for intracellular recording: the freshwater turtle (Pseudemys scripta elegans) and tiger salamander (Ambystoma tigrinum). Technical innovations include: (1) the use of lasers to simultaneously measure dark adaptation and photopigment regeneration in cone photoreceptors and (2) the use of a Liquid Crystal Display (LCD) to apply patterned light stimuli on the retina. Many of the experiments parallel human psychophysical work so the results could lead to new models for clinical disorders in contrast perception and dark adaptation. Mechanisms of visual adaptation will be analyzed in a series of experiments that will investigate the relation between photopigment regeneration and recovery of cone sensitivity, the equivalent background hypothesis, and properties of rapid dark adaptation. Mechanisms for contrast vision will be investigated via recordings from bipolar and amacrine cells. Contrast or response curves will be analyzed in detail to understand how contrast is encoded and transformed in the retinal network.